AC Lim's answer to Dylan Ang's Primary 6 Maths Speed Singapore question.
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Hope this helps
Date Posted:
3 years ago
But the 19 is the total black blocks not both the blocks...
Very simple.
Every 3 white must be flanked by 2 black blocks.
We can see that the pattern repeats. We can group every 3 white blocks with 1 black block.
The last black block is alone and does not have 3 white blocks after it. It is only use to flank the 3 white blocks before it.
Every 3 white must be flanked by 2 black blocks.
We can see that the pattern repeats. We can group every 3 white blocks with 1 black block.
The last black block is alone and does not have 3 white blocks after it. It is only use to flank the 3 white blocks before it.
So only 18 black blocks are grouped with white ones.
(19 - 1 = 18)
This means there are 18 groups.
So since there are 3 white blocks in each group,
Number of white blocks used
= 3 × 18
= 54
(19 - 1 = 18)
This means there are 18 groups.
So since there are 3 white blocks in each group,
Number of white blocks used
= 3 × 18
= 54
This is how it looks like :
(1)-----(2)------(3)-----(4)------(5)... ... ....(17)-----(18)----(19)
■□□□■□□□■□□□■□□□■......□□□■□□□■□□□■
(1)-----(2)------(3)-----(4)------(5)... ... ....(17)-----(18)----(19)
■□□□■□□□■□□□■□□□■......□□□■□□□■□□□■